Now that “Metropolis” is nearly complete, and Louise Brook’s “Pandora’s Box” still survives, I would really like to see Theda Bara’s “Cleopatra”. For the sake of the costumes, if not for anything else.
Wings with its original soundtrack (which won it the Oscar). The original records do still exist, but it’s a case of a certain type of historical society lady who is in charge of the archive and not allowing anyone near the recordings (if she doesn’t downright insist that the records do not exist if you’re not the ‘right’ kind of person.)
I just wanted to say that this is why I love this place. Here’s a poster that’s been around eight years, has less than two hundred posts, yet knowledgeably chimes in on a post that piques his or her interest. I find these instances fascinating. Sorry for the hijack.
Quite all right. Reclusive people often have very special knowledge.
I’d like to see the newsreel version of NBC’s first TV broadcast in 1936. RKO Pathé News filmed it as it was being broadcast live, with a movie camera right beside the TV camera. RKO handed over the reel to their parent RCA, who wanted it for a screening for bigwigs who hadn’t been able to make the live show. It was subsequently “lost,” but seeing as the show was so top secret that even the press weren’t invited, it was probably burned.
Hoarders. Hate 'em. It was my great pleasure to demolish a largish and very self-satisfied group of such, a decade or so back.
This.
Santo Gold’s immortal Blood Circus. I’d love to see it, and if I had a million dollars I’d have Joel and the 'Bots do their thing over top of it.
I’d like to see the dailies, production stills, or read the script to Alejandro Jodorowsky’s Dune, which was to star Orson Welles and Salvador Dali, with a score by Pink Floyd. Heck, I’d like to hear the music.
Sadly, the financial backers backed out half way through and we ended up with Alien instead.
Many of the above, plus the 1916 version of Under Two Flags, with Theda Bara.
Hat’s Off, early Laurel & Hardy short, and the first where they played more or less their famous Stan & Ollie characters. . The Music Box, where they famously carry a piano up a long flight od steps, is a remake.
There’s a lot of “Lost” films I’d love to see but one which springs to mind (and doesn’t appear to have been mentioned yet) is The Life of General Villa, the film of the Mexican Revolution which starred Pancho Villa as himself*. They actually filmed some of the (real) battles and got Villa’s army to re-stage others - I’m sure it’d be interesting, not to say historically fascinating, stuff.
*There was a movie in 2003 called And Starring Pancho Villa As Himself about this, with Antonio Banderas in the lead role.
You can see some of the production sketches in back issues of Cinefantastique devoted to the movie Dune. I know a lot of people go nuts over this one, but I’m pretty skeptical myself about how it would have turned out.
Not only Pink Floyd. Tangerine Dream and another band were supposed to do the music. Apparently, each major planet would have been covered by its own band.
It’s the Ultimate House Band!
Yes, I am happy to contribute whatever I can, and a big thank-you to you others who have contributed much more.
I don’t know the titles, but I know who starred in them! 
And about what year they came out.
Seriously, just kidding. 
Yeah, more in the spirit of the OP and some other posts – I think a lot of Ford silents have been lost, as have those of Lubitsch. I’d much rather see the Lubitsch 1920s films, but it could be instructive to watch the work of even well-documented workhorses like Ford and Hawks. To my knowledge, there’s only been one (or perhaps a small handful of) serious scholarly monographs/books on Lubitsch.